The present invention relates to lasers, and, in particular, to chemical laser devices which operated with a plenum chamber which is provided with gases which are heated by combustion or other means to produce atomic or free radical species. For example, F.sub.2 is heated to give F-atoms. Diluent gases such as He or N.sub.2 are also added and heated in the plenum. Following the combustor plenum, the gases are expanded through a supersonic primary nozzle to a high velocity and low pressure. The gases exit this nozzle to a lasing cavity. H.sub.2 and D.sub.2 gases, for example, are injected into the cavity and mixed with the expanded F-containing free jet. The reaction with F-atoms initiates the chemical pumping mechanism which yields vibrationally excited HF or DF. Mirrors are placed about the cavity and lasing results from the vibrationally excited HF or DF. The gases are then pumped to a pressure such that atmospheric exhaust is possible.
Aerodynamic considerations dictate the dimensions of the primary nozzle and together with the high plenum temperatures required for lasing operation give rise to severe viscous effects in the supersonic primary nozzle. With He as a diluent and combustor plenum temperatures in excess of 1000.degree. K., it has been found that the flow exiting from the primary nozzles of working devices is totally viscous, i.e., the influence of the wall drag is distributed throughout the jet flow. The detrimental aspects of the viscous flow are a loss in total pressure, a decrease in the gas exit velocity and an increase in gas exit temperature, i.e., a decrease in Mach number. The attendant decrease in initial Mach number of the reacting streams dictates large quantities of diluent gases be included to prevent thermal choking of the flow in the presence of heat addition. Loss of total pressure and increased diluent ratios give rise to increased pumping requirements. Either a decrease in gas velocity or an increase in gas exit temperature lead to a reduction in the length of the gain supporting laser region with consequent degradation of laser beam coherence and increased mirror loading.
An improved CW chemical laser causes the gas flow to become supersonic before it enters the region of the H.sub.2 or D.sub.2 injector tubes. Because the supersonic flow is brought about in a large nozzle, viscous effects in producing the supersonic flows are minimized. Wedge shaped devices used for the H.sub.2 or D.sub.2 injectors do, however, create both viscous drag and wave losses because the wedge shaped devices are located downstream of the primary nozzles and in the supersonic gas flow. The net results is that the lasing efficiency is less than 50% of the theorictically achievable efficiency.
Therefore, it can be clearly seen that there is a need for a better nozzle arrangement for introducing the free radical species with the secondary gases of D.sub.2 or H.sub.2.